A shift switching control device of a vehicle is well known that includes a shift switching mechanism that electrically switches a shift position of an automatic transmission with activation of a step motor based on an operation signal indicative of an operating state of an operating device for switching a shift position of the automatic transmission. This is a shift switching control device called shift-by-wire (SBW), for example, and corresponds to a shift range changing device of an automatic transmission described in Patent Document 1 and a shift switching device described in Patent Document 2.
In Patent Document 2, a three-phase switched reluctance motor (SR motor) is exemplarily illustrated as a step motor (stepping motor) acting as a drive source of a shift switching mechanism. Such a step motor can employ an excitation mode such as a one-phase excitation mode in which a current is sequentially applied only to one phase of windings as depicted in FIG. 9(a), a two-phase excitation mode in which a current is sequentially applied to two phases at the same time as depicted in FIG. 9(b), and a one-two-phase excitation mode in which one phase and two phases are alternatively switched to sequentially apply a current as depicted in FIG. 9(c), for example. In FIG. 9, for example, the excitation patterns of the excitation modes are set such that a step angle (rotation angle) per unit time of a rotor of a step motor is set to the same angle θ, i.e., the same motor rotation speed is achieved. Particularly if the one-two-phase excitation mode is employed, the excitations pattern is formed by combining the one-phase excitation and the two-phase excitation and, therefore, a step angle corresponding to a reference pulse is halved as compared to the case of the one-phase excitation mode or the two-phase excitation mode, thereby enabling smooth and fine motor rotation control. An output torque of the step motor becomes relatively large.